Improvement in balanced slide-valves



UNITED STATES PATENT OFFICE.

JOHN ROVBOTHAM, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO HIM- SELF ANDANDREW J. DESHER, OF SAME' PLACE, ASSIGNORS 'IO SAID ROWBOTHAM AND JAMESH. SPENCER, M. D., OF SAME PLAGE.

IMPROVEMENT IN BALANCED SLIDE-VALVES.

Specification forming part of 4Letters Patent No. 51,393, dated December5,1865.

, ter, so as to form a steam-tight joint between the valve and top ofthe steam-chest.

My invention further consists of certain recesses formed in the saidstrips and communieating with the exhaust-chamber of the valve,substantiallyas described hereinafter, so that there may be a sufficientpressure of steam against the strips to insure tight joints withoutcausing undue friction.

My vinvention further consists of certain springs, arrangedsubstantially as described hereinafter, for maintaining the said stripsin contact with the valve and steam-chest cover.

My improved valve is so limited in dimensions that it can be readilyapplied to any ordinary steam-chest without altering the same, and theaforesaid strips, being capable of independent movement, will readilyaccommodate themselves to any unevenness in the arrangement of thesteam-chest cover.

In order to enable others skilled in the art to make and apply myinvention, I will V110W proceed to describe its construction andoperation.

On reference to the accompanying drawings, which form a part of thisspecification, Figure lis a planview of my improved balanced slidevalve;Fig. 2, a transverse vertical section on the line 1 2, Fig. 1; Fig. 3,an edge View; and Fig. 4. a section of the strips on the line 3 4, Fig.1.

Similar letters refer to similar parts throughout the several views.

The body of the valve consists of an oblong base, A, open at the top andbottom, and having at the lower end, on all four sides, a lip or flange,a, the width of the exhaust-openingbetween .r and y, Fig. 2, and thewidth of the valve across the anges, heilig so adapted to thesteam-ports l and b', and exhaust-ports d on the valve-seat B, as toinsure the proper lap and lead.

The height of the body A of the valveis such compared with the depth ofthe steam-chest that the upper edge of the said body shall always befree from contact with the under side otl the steam-chest cover D.

The four sides of the body of the valve at the upper edge of the sameare made perfectly true, so as to form steam-tight bearing-surfaces forthe end strips, E and E,and side strips,Fand F', the ends of the formerresting on lips q formed on the ends of the latter, as seen in Figs.3and 4., and the ends 'of the strips F and F bearing against the sidesof the strips E and E', as seen in Fig. l. In order to maintain thesestripsin contact with the body of the valve, I use in the presentinstance the springs G, each of which is secured to one of the strips For Ff, and is so bent at the outer end as to lit into a notch in theadjacent strip E or E', the action of the whole of the four springsbeing such as to press the strips tight against the body of the valve.V

Between the iiange a and the strip F intervene two springs, H H, similarsprings intervening between the ilange on the opposite side of the valveand the strip F', these four springs tending to press the whole of thestrips upward against the under surface Yof the steamchestcover.

It will be observed that in the upper surface of each of the strips is arecess, m, and that there is a similar recess, n, in that side of eachstrip which bears against the body of the valve. Each of these recessesm and n communicates, through any suitable openings, p p, in the bod yof the valve, with the exhaust-space M.

It should be explained here that, although I use springs which willmaintain the strips in contact with the steam-chest cover and body ofthe valve, I do not rely upon these springs alone for the exertion ofthat force necessary to maintain the strips in steam-tight contact withthe cover and valve, the steam itself being relied upon to furnish thisforce, while the springs themselves act as auxiliaries, their mainobject being to keep the parts together in adjusting the valve to itsplaccin the iirst instance. rEhe pressure of the steam against the underside of the strips would not maintain them in tight contact with thecover Without the use of the recesses m m, which communicate with theexhaustchamberM of the valve. It will be evident that as the area ofthese recesses is increased the greater will be the force exerted by thesteam to press the strips upward, and that the extent of the area ofthese recesses may be such as to obtain the desired bearing force of thestrips against the cover, to insure a perfectly steam-tight jointwithout causing undue friction.

The same remarks will apply to the recesses a a on the sides of thestrips, which recesses also communicate with the exhaust-chamber M ofthe valve. The greater the extent of the area of these recesses thegreater will be the pressure of the strips against the valve.

In ordinary slide-valves the exhaust-chamber is closed at the top bypart of the valve itself. These valves are apt to j ump at the time theexhaust-steam is leaving` the cylinder, and

' strike the under side ofthe valve, this jumping or rising of the valvetaking place invariably at the same points in its stroke, so that theseat of the valve must of necessity be nnevenl y worn; hence theimportance ofa valvein which the exhaust-chamber is open at the top, or,in other words, a valve in which the top of the exhaust-chamber isformed by the steam-chest cover against which the exhaust-steamimpinges, Without affecting the proper position of the valve on theseat.

The unpopularity ot' this class of valves appears to be owing to thedi'lcnlty of maintaining` a perfectly steamtight joint between the topof the valve and the steam-chest cover Without the employment ofcumbrous appliances Which cause excessive friction. Itwill be seen fromthe foregoing description that the strips afford a perfectly tightjointbetween the valve and the steam-chest cover, and this without causingundue friction.

An important advantage of my improved valve is its limited dimensionscompared with other balanced slide valves, the valve being such that itcan be applied to any ordinary steam-chest without altering the same.

A further advantageis this, thatif the steamchest cover be not exactlytrue or parallel with the face of the valve the strips, being capable ofmoving independently of each other, Will readily accommodate themselvesto such inequality without disturbing the integrity ofthe joints.

Should steam, through imperfect Workmanship or other cause, pass fromthe chest through thejointbetween the strips and steamchest cover, thissteam can in no way affect the valve, as it passes off at once throughthe exhaust-opening without exerting the slightest pressure on the valveitself.

I claim as my invention, and desire to secure by Letters Patentl. Aslide-valve having,` an exhaust-chamber open to the steain-chestcover,in combination with strips adapted to each other and to the said valveand cover, substantially as and for the purpose described.

2. The arrangement of the recesses formed in the said strips andcommunicating with the exhaust-chamber, substantially as specified.

3. The combination of the said strips with springs G, constructed andapplied to the said strips, substantially as set forth.

4. The combination of the body of the valve, the strips, and the springsH, or their equivalents.

In testimony whereof I have signed my name to this specilication in thepresence of two subscribing witnesses.

JOHN ROWBO'IHAM.

Witnesses:

H. HoWsON, JOI-1N WHITE.

